Experimental Study of the Variation in Oscillation Characteristics of Point-Contact-Based Spin-Torque Oscillators

This paper presents an experimental study of the variation in oscillation characteristics of circular point-contact-based spin-torque oscillators (PC-STOs). We first measured the oscillation behavior of multiple, identically fabricated PC-STOs, then made the same measurements on a PC-STO and rotated the azimuth angle of the bias field $\varphi$ . Our results show considerable device-to-device variations among identical PC-STOs. More striking is large changes within a single PC-STO for a small $\varphi$ rotation, which is totally inconsistent with the geometrical symmetry of the device. These results suggest that the giant magnetoresistance stack has some form of microstructural inhomogeneity, which causes a strong $\varphi$ dependence of the oscillation behavior, eventually resulting in the device-to-device variation. Some possible sources of the inhomogeneity are discussed based on these observation results.